Geothermal system and tubing therefor

ABSTRACT

A geothermal heat pump has a pump. A tubing conveys a fluid from the pump and adapted to transfer energy between the fluid and the ambient environment as the fluid travels through the tubing. The tubing has a high thermal conductivity.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.61/226,561 filed on Jul. 17, 2009 in its entirety.

BACKGROUND OF THE INVENTION

This invention is directed to a geothermal system, and more particularlyto the fluid transfer structure therefor.

Geothermal energy systems are known in the art. By way of example ageothermal heat pump utilizes the ground temperature to heat or cool afluid through energy transfer with the ground to regulate the interiortemperature of a facility. The system uses the earth as either a sourceof heat in the winter or as a coolant in the summer. The geothermal heatpumps take advantage of substantially consistent moderate temperaturesin the shallow ground to boost efficiency and reduce operational cost.The temperature of the ground remains fairly constant except for veryclose to the surface while the temperature of the air above ground, andwithin a facility, changes relatively dramatically.

During the summer, the ground temperature below the surface is normallycooler than the ambient temperature above ground. In the winter, forthose countries above the equator, the opposite is true and thetemperature below the ground, particularly in northern climates, iswarmer than the ambient temperature above ground. To maximize theoperation of the geothermal system, the system must take advantage ofthe temperature differential across all seasons.

The geothermal heat pumps include a pump which pumps fluid throughtubing. The tubing extends through the ground and exchanges energy withthe ground to enable the fluid to either lose or gain heat dependentupon whether the temperature of the fluid is greater than or less thanthe temperature of the ground through which it passes. The fluidconveying system then carries the fluid back to the home or facilityabove the ground to control the environment therewithin. It is known inthe art to use plastic tubing to convey the fluid through the ground.

These systems, although rudimentary have been satisfactory, but fairlyinefficient. First, the materials used have a low thermal conductivity,so that the necessary heat exchange between the ground and the fluid isdifficult, requiring a longer run of tubing within the ground tomaximize energy transfer.

Furthermore, energy is wasted because the thermal conductivity is notsufficiently high to maintain the temperature of the fluid for longstretches of travel through the ground. Therefore, the transfer ofenergy between the ground and the fluid continues, so that on the returntrip to the facility the fluid is either heating or cooling the ground.Accordingly, a system which overcomes the shortcomings of the prior artis desired.

BRIEF SUMMARY OF THE INVENTION

A system is provided having a pump. The pump is operatively coupled to atubing having made of a high thermally conductive material. The tubingis adapted to promote the transfer of energy between a fluid containedtherein and earth surrounding the pipe.

In one embodiment, the tubing is made from a high density polyethylene.In another embodiment the tubing has a thermal conductivity of about 0.4W/(m−K). In another embodiment, the pipe includes a first section madeof a high density polyethylene and a second section. The first sectionhas a thermal conductivity one and a half to five times as great as thethermal conductivity of the second section.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is had to thefollowing description, taken in connection with the following drawingsin which:

FIG. 1 is a schematic drawing of a heat pump constructed in accordancewith the invention; and

FIG. 2 is a schematic diagram of the fluid conveying section of the heatpump constructed in accordance with a second embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made to the FIGS. 1 and 2 in which a geothermal heat pump,generally indicated as 10, is provided. Heat pump 10 includes a pump 12for pumping a fluid. A pipe, generally indicated as 14 conveys the fluidfrom pump 12 in the direction of Arrow A. At least a portion of the pathof pipe 14 is through ground 100 near the facility (a house, building orthe like) 102 to be controlled by heat pump 10. In a preferredembodiment, pipe 14 is a plastic tubing.

In one embodiment of the invention, pipe tubing 14 is formed of a highdensity polyethylene (above 0.940 g/cm³) having a high thermalconductivity, preferably about 0.5 W/(m−K) or higher, and preferably,about 0.7 W/(m−K) or higher.

At the depths through ground 20 through which tubing 14 will travel, thetemperature of the earth reaches about 8° C. The desired temperature ofthe fluid approximates that of the temperature of the ground at thedepth to which the tubing 14 travels.

The temperature of the ground changes, from the ambient temperature, asseen in FIG. 2, at the surface of the ground to the desired temperaturebeneath the surface. Therefore, to maximize the heat transfer efficiencyin accordance with the invention, the fluid is exposed to a temperatureof the ground as long as necessary until the temperature of the fluidapproaches a desired temperature differential.

However, as is known in the prior art systems, the fluid travelingthrough tubing 14 continues to exchange energy with the ground on itsreturn trip as it traverses the ground temperature gradient on thereturn to the environment to be controlled. Accordingly, in a preferredembodiment, tube 14 includes a first section 18 and a second section 20.First section 18 has a significantly higher thermal conductivity thansecond section 20 significantly greater than 0.45 W/(m−K). Secondsection 20 is downstream of the fluid and sufficiently downstream of thereturn point of the path of tubing 14 (that point in which tubing 14begins its final path towards surface 104) of ground 100.

As tubing 14 returns to the surface, the temperature gradient of theground approaches that of the surface temperature. As a result, thefluid will exchange energy with the ground to either lose or gaintemperature as it experiences this new temperature gradient.Accordingly, second section 20, having the lower thermal conductivityless than 0.3 W/(m−K), in order to prevent such temperature exchangewithin a fluid, should begin at a point between the return of tubing 14to the surface and a position where the temperature gradient will resultin a changing temperature of the fluid within tubing 14. In this way,the exposure of the fluid to the desired ground temperature is maximizedand the possibility of energy transfer to lose the desired temperatureis minimized.

In a preferred embodiment, the thermal conductivity of first section 18is substantially higher than that of second section 20. In a preferredembodiment, the thermal conductivity of first section 18 is one and ahalf to three times greater than the thermal conductivity of secondsection 20. In a still further preferred embodiment, the thermalconductivity of second section 20 is about 0.3 W/(m−K) or less. Secondsection 20 which thermally isolates the fluid contained therein may bemade of a low density polyethylene or a polypropylene; significantlyless than 0.940 g/cm³.

During use, a fluid is pumped through tubing 14 in the direction ofarrow A. As fluid traverses through section 18, the temperature of thefluid approaches, through thermal exchange with the ground, that of theground. At the return, point F in this embodiment, the fluid passesthrough second section 20 before the temperature of the fluid hassubstantially changed.

It is to be understood that although used by the invention, that theground and the fluid make up no part of this invention.

It will thus be seen that the objects set forth above, and those madeapparent from the precedent description, are efficiently obtained and,since certain changes may be made in the above construction withoutdeparting from the spirit and scope of the invention, it is intendedthat all matter contained in the above description and shown in theaccompanying drawings, shall be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are intended tocover all generic and specific features of the invention hereindescribed and all statements of the scope of the invention which, as amatter of language might be set to fall therebetween.

1. A geothermal heat system having a pump, and a tubing of high thermalconductivity in fluid communication with the pump for conveying a fluidfrom the pump and adapted to transfer energy between the fluid and anambient environment as the fluid travels through the tubing.
 2. Thegeothermal heat pump of claim 1, wherein the ambient environment is theground.
 3. The geothermal heat pump of claim 1, wherein the tubing has afirst section and a second section, the first section having a thermalconductivity substantially greater than the second section.
 4. Thegeothermal heat pump of claim 3, wherein the tubing includes a return,the second section being downstream of the return.